1. Field of the Invention
The present invention relates to a laminate of a liquid crystalline polyester layer with a copper foil which can be used as, for example, a flexible wiring substrate.
2. Description of the Related Art
A laminate with a copper foil is widely used as a flexible wiring substrate in electronic devices in which high density mounting is required.
Especially, a copper-foil laminate having a liquid crystalline polyester layer as an insulating resin layer attracts attention as a substrate for electronics because of an excellent high frequency characteristic, a low water absorption property and the like due to the properties of liquid crystalline polyester.
In the case that a liquid crystalline polyester layer (or film) to be used in a laminate is produced by an extrusion molding, the layer may be oriented in the direction of the extrusion, and therefore, may have large anisotropy in the longitudinal direction (i.e., the direction to the extrusion) and the transverse direction (i.e., the perpendicular direction to the direction of the extrusion). Such a liquid crystalline polyester layer may have a low mechanical strength in transverse direction compared to that in longitudinal direction, a different adhesion with a copper foil depending on directions, and a different dielectric constant depending on directions, which may make design of a circuit board made from the resulting laminate difficult.
In regard with a liquid crystalline polyester layer, a layer having good properties for a copper-foil laminate has been proposed in which a liquid crystalline polyester solution of a liquid crystal aromatic polyester and an aprotic solvent with no halogen atom is utilized (Japanese Patent Application Laid-Open (JP-A) No. 2004-315678, corresponding to US 2004/0210032 A1).
On the other hand, a flexible copper-foil laminate is also requested so that it may be endured for the use in high frequency. This is because in recent years, many portions of the copper-foil laminate stored in an electronic device may be bent so often, the angle of the bending portions may become small, and the copper-foil laminate is widely used for the places where wiring are needed such as the operating part in a drive member of an electronic device.